Tamper detection in Automatic Meter Reading/Advanced Metering Infrastructure (AMR/AMI) electric meters has previously often consisted of a mechanical sensor that changes state when tilted more than a predetermined number of degrees. Such “tilt” sensors were used in conjunction with power-down and power-up of the electric meter as an indicator whether the product “may” have been tampered with. Two indicators are currently provided in Itron's OpenWay CENTRON AMI meter, namely, removal and inversion.
Likewise, invocation (i.e., selection) of alternate display sequences in electronic meters has previously been achieved through the use of mechanical switches and later by magnetic switches. Both of such devices have a cost associated with them and have functional limitations. Mechanical switches bear additional product cost and use up portions of limited real estate on the face of the product. A magnetic switch approach is quite effective but requires utility field personnel to carry a magnet to the field to invoke the display sequence of interest which also bears additional product cost as well as inconvenience.
It is desirable that meters in the field support reliable detection of inversion and removal tampers. Some previous configurations used an optical roll ball switch to detect tampers. Although such a switch works in most cases, it does possess several limitations. First, it requires that the socket be installed as vertically as possible and cannot tilt more than a predetermined amount. In exemplary installation the meter should not tilt more than twenty degrees. Second, the detection is very sensitive to the angle in which the socket tilts. Third, due to the switch's limited angle range, a removal tamper in which the tilting angle is less than a predetermined amount (for example, twenty degrees in an exemplary configuration) would not be detected.
Known patents related to the present field of inquiry include U.S. Pat. No. 7,495,555 to Seal et al., directed to “Magnetic Field Sensing For Tamper Identification,” U.S. Pat. No. 7,453,373 to Cumeralto et al., directed to an “Integrated Meter Module And Utility Metering System,” U.S. Pat. No. 6,852,935 to Higgins et al., directed to a “Tilt Switch,” and U.S. Pat. No. 5,910,774 to Capriotti et al., directed to a “Sensor For Count And Tamper Detection.” Each of such patents is owned by the owner of the present subject matter and is fully incorporated herein for all purposes.
While various implementations of tamper detection systems have been developed, and while various combinations of tap responsive devices have been developed, no design has emerged that generally encompasses all of the desired characteristics as hereafter presented in accordance with the subject technology.